Vibration-resistant playback device having reduced power consumption

ABSTRACT

A control unit sets a first reading speed and a second reading speed of the information stored on the information medium as a function of a predetermined occupancy of the buffer below its storage capacity. The drive motor, which produces the reading speed, is connected via a switch to the driver which drives it and, during a reduction of the reading speed to a predetermined value or until the occupancy of the buffer falls below a predetermined occupancy, the power supply to the drive motor which produces the reading speed, is reduced by means of the switch for the purpose of reducing the power consumption.

This is a division, of application Ser. No. 08/568,126, filed Dec. 6, 1995.

BACKGROUND OF THE INVENTION

The invention relates to a method and an arrangement for a vibration-resistant playback device having a reduced number of returns and having a reduced power consumption. The field of application of vibration-resistant playback devices applies, in particular, to the portable and mobile use of playback devices of optical information media, in which uninterrupted and undisturbed reproduction of information must be ensured despite vibrations, the field of application not being restricted, however, to optical information media.

Optical scanning devices, in particular, are sensitive to mechanical vibrations, since the optical scanning system can be pitched from the track by vibrations and, as a result, the read operation of the information stored on the information medium is interrupted. During stationary operation, these vibrations are so small that they can be adequately damped by means of mechanical precautions and electrical control loops. However, in the case of mobile use, such as, for example, in a car, or in the case of portable devices, the abovementioned measures no longer suffice, and use is made of a buffer which buffers the data stream for the purpose of reproduction during an interruption of the reading of the information medium. A buffer of this type is known in accordance with the data sheet of the CXD2511Q/R circuit from Sony (Vibration-Protective Memory Controller for CD Players). In order to provide a data reserve, the data are read from the CD at twice the speed and are stored in the buffer. At the same time, data are read at normal speed from the buffer for the purpose of reproduction. In order to prevent an overflow of the buffer, the reading of the information medium or the writing of data to the buffer must be continuously interrupted and the read operation must be resumed after the occupancy of the buffer has fallen below a minimum occupancy. For this purpose, the scanning or reading system must be returned to the location of the interruption and the reading of the information medium must be continuously resumed. This sequential pattern of events is continued unremittingly provided that no vibration occurs. As a result, a high number of resets or returns of the scanning or reading system are already necessary during vibration-free operation. If a vibration occurs during a reading pause, no special measures are necessary.

However, if the vibration occurs during the read operation, then the filling of the buffer must be stopped immediately and the scanning system must be returned as quickly as possible to the location at which the read operation was interrupted, in order to read anew data from the information medium or the CD. Following successful conclusion of this operation, the filling of the buffer is resumed. Consequently, this jumping or resetting of the scanning system to the location of the interruption of the reading of the CD is not only necessary when vibrations occur but also necessary when vibrations do not occur in the vibration resistance mode of operation, since the read operation which is carried out at twice the speed must be interrupted when the buffer is full.

In order to write data from the information medium to the buffer following an interruption in accordance with the order present on the information medium, the reading of the CD is resumed using data prior to the last subcode address evaluated as valid by a microprocessor, and in order to start the writing to the buffer, or for the sequentially correct resumption, a comparison between the stored and the read audio data is carried out. This audio data comparison, which controls the resumption of the writing to the buffer in the event of a positive result, is carried out after the decoding and error correction and directly before the digital/analog conversion. The buffer is connected to the de-interleaving and error correction unit of the decoder and is arranged directly before the digital/analog converter.

In addition to the relatively high number of returns when no vibrations occur, a problem of this solution is the reliability of the data synchronization for starting the write operation to the buffer. The synchronization which is based on the audio data comparison is not always successful, since, owing to errors, the data bits do not always appear in the same way and accurately timed. A chronological offset also occurs when comparing very soft passages, in which only zeros are compared, or when comparing passages which contain multiple repetitions such as, for example, a sinusoidal tone at a specific frequency. The data comparison which must be carried out frequently in connection with the interruptions does not guarantee the determination of the exact synchronization instant, leads to jumps in the audio data and consequently, owing to chronological jumps in the title or disk time, does not ensure accurately timed reproduction corresponding to the stored information.

A further problem is constituted by the power consumption associated with the doubled reading speed and the frequent track jumps. The service life of batteries in portable devices is reduced approximately by half due to the decoding at twice the speed and an increased number of actuator control operations. This increased power consumption occurs even during operation without any vibrations, since the reading of the CD at twice the speed requires an interruption of the write operation and resetting or reversing of the scanning unit. Moreover, a DRAM must be provided as the buffer for the most precise data comparison possible, and it represents a considerable cost factor.

The strength to withstand shocks and vibrations acting on the device from the outside is of crucial significance for the functionality of portable CD players. In order to enjoy CDs when jogging, it is known to provide a "digital shock absorber", cf. Walter Schild: A digital shock absorber in order to enjoy CDs when jogging, in the daily newspaper Die Welt, dated Jul. 16, 1992. In order to permit undisturbed and uninterrupted reproduction of information despite a brief interruption in the scanning of information from the CD as a result of a shock which causes the laser or scanning beam to lose the information track, the CD is driven at twice the speed and data read from the information medium are buffered. Data are then available from the buffer for the undisturbed reproduction of information during the period of an interruption. This property of portable CD players is therefore also referred to as so-called "shock-proof memory" or "shock-protection memory". The disk which is driven at twice the speed supplies data twice as fast as is necessary for the reproduction, with the result that the buffer is rapidly filled with data once more even after an interruption. In this case, however, the driving rotational speed is not constant, since CDs are read at a constant linear velocity, the so-called CLV. Since the CD has a smaller number of pits in the inner region of the disk than in the outer region, for one revolution, the driving rotational speed of the disk turntable is correspondingly reduced when reading from the inner to the outer region in order to ensure a constant reading speed. In this case, a constant reference frequency corresponding to the reading speed is used to control the rotational speed. The current speed information is taken from the frequency of the signal scanned from the information medium, which frequency forms the so-called actual value in the control loop.

If the buffer is completely full, the reading in of data is interrupted until a predetermined occupancy which warrants the further reading in of data is reached. During this time, too, the information medium is driven at twice the speed and the scanning speed is controlled by the control loop to a constant linear velocity CLV. The interruption of the read-in operation causes frequent track jumping and frequent rotational speed changes even without the occurrence of disturbances, since the scanning of the information medium following an interruption of the read operation must be resumed at a point at which the read operation was previously interrupted. The frequent track jumping and the driving of the information medium at twice the speed result in an increased power requirement, which has a particularly disadvantageous effect on the total playing time which can be attained by batteries. The total playing time which can be attained using a set of batteries in shock-proof operation is reduced approximately by half in comparison with normal operation at normal scanning speed on account of the drive at twice the speed, decoding of the scanning signal at twice the speed and an increased number of movements of the actuator or scanning system owing to increased track jumping.

Therefore, the object of the invention is to reduce the number of returns and to avoid the abovementioned disadvantages of the known solution and to provide a vibration-resistant playback device which has a low power consumption despite ensuring the "shock-proof memory" function.

This object is achieved by means of the features specified in independent claims. Advantageous refinements and developments are specified in dependent claims.

The invention is based on a vibration-resistant playback device which is operated predominantly at normal playback speed despite ensuring protection against vibrations, and in which there is no interruption of the read operation from the information medium in the event of operation without any vibrations, as a result of which frequent track jumping is avoided and the power consumption is considerably reduced. Furthermore, the reliability and accuracy of the data synchronization following a vibration-induced interruption can be increased, and use can be made of a buffer which is less expensive than a DRAM. These advantages are achieved by means of an arrangement and a method for controlling the reading speed from the information medium as a function of a predetermined occupancy of the buffer below its maximum storage capacity, the control arrangement varying the reading speed from the information medium in order to store a predetermined amount of data in a buffer without interrupting the reproduction before said data is read from the buffer. Overflowing of the buffer or the situation where the occupancy of the buffer falls below a minimum occupancy is prevented without interrupting the reading from the information medium by the fact that a reading speed which is increased in order to fill the buffer is already reduced to normal speed at a predetermined occupancy of the buffer below its maximum storage capacity, and the number of returns is reduced thereby. In contrast with reading the information medium at twice the speed, a reading speed in the region of the normal speed is set, which speed is preferably the conventionally used normal speed in playback devices without special vibration protection, when the occupancy of the buffer has not fallen below a predetermined occupancy. Only during the filling of the buffer is use made of a reading speed which is above the normal speed, but preferably without any loss in the bit timing of the phase control, until a predetermined occupancy of the buffer is reached. Resetting or returning of the scanning or reading unit is no longer necessary in order to produce the preconditions for vibration resistance, as a result of which the power consumption is considerably reduced. The increase in the reading speed without any loss in the bit timing which is required for processing the information from the information medium is made possible by a bit timing PLL having a relatively large capture range. This capture range is preferably more than ±60%. In order to reduce frequent changing over of the reading speed in connection with the occupancy of the buffer falling below and exceeding a predetermined occupancy, and in order to reduce the power consumption further, a first and a second occupancy are preferably used as the predetermined occupancy. If the buffer is full, it becomes necessary to change over the reading speed only in the event of vibration, since the read-in and read-out speeds are identical. The occupancy changes at normal speed. The reading speed is then accelerated when the occupancy falls below a first occupancy, and is not reduced until the second occupancy value is reached. In this case, the second occupancy value is selected in a manner analogous to control as a function of only one occupancy in such a way that the buffer is likewise filled only to its maximum capacity during the transition from an increased speed to the normal speed. The use of a first and a second occupancy value results in a hysteresis which leads to greater running smoothness. The control arrangement is preferably implemented as part of the decoder, and the buffer is preferably arranged between the EFM demodulator (EFM=eight to fourteen modulation) and the de-interleaving and error correction unit which provides the digital information. This arrangement enables simple processing of subcode information such as, for example, information regarding time and location, which then only have to be processed at normal speed in the decoder and can advantageously be used for the data synchronization. Decoding at twice the speed is unnecessary, since the buffer acts as a time base compensation element. The subcode can also be read and evaluated at a variable reading speed in the PLL capture range. The time information, that is to say the title or disk time corresponding to precisely that music which is to be heard, is calculated from the instantaneously read subcode and the occupancy. The already known data comparison with the disadvantages specified could also be used for the synchronization or for the writing of data to the buffer without any gaps. However, it is advantageous to use for the synchronization subcode data, preferably the synchronization word or synchronization bits, which are present in the data stream. Although the subcode data are available at different points in time, particularly as a result, too, of the reading speed which is adapted to the occupancy of the buffer, and only occur at relatively large spacings, reliable synchronization and a seamless data flow following an interruption are achieved by the fact that use is made of an item of address information which identifies the interruption location prior to the error correction in the data stream. The starting point of the synchronization is formed by a valid subcode, the address information of which can be used as a reference both for the location of the interruption on the information medium and for the last valid data in the buffer and the writing to the buffer. Using the address which identifies the location of an interruption on the information medium and in the buffer, the synchronization and the writing to the buffer after an interruption can also be implemented even before the address of the interruption, since the spacing between the last valid address, which corresponds to the synchronization byte of the last valid subcode, and the new address, which corresponds to the synchronization byte of the new valid subcode, can be calculated. The data following the address are then overwritten, resulting in a shorter time to synchronization. For this purpose, the buffer is preferably arranged upstream of the error correction and de-interleaving unit.

A data comparison is not carried out and a seamless data flow is, nevertheless, reliably achieved, despite a varying reading speed, particularly as a result of the fact that the buffer simultaneously serves as a time base compensation unit and data are read at a constant speed from the buffer.

On account of the arrangement of the buffer between the EFM demodulator and the de-interleaving and error correction unit which provides the digital audio information, it is possible to use an ARAM, which is less expensive than a DRAM. The use of an ARAM or audio RAM, which may be partially defective, is made possible by the arrangement before the error correction.

In addition to reducing the number of returns or the number of repositionings of the scanning or reading system, also referred to as a pick-up, in vibration-resistant playback devices by controlling the reading speed of the information medium as a function of the occupancy of the buffer, further aspects of the invention comprise the rapid availability of data for the reproduction after a start and the data synchronization. The number of necessary synchronization operations is already reduced by the smaller number of returns and their accuracy and reliability can be increased further. In order to reduce the power consumption of vibration-resistant playback devices, a power supply-reducing means is furthermore provided, by means of which the power supply to the drive motor of the information medium is temporarily interrupted or at least reduced. If a stationary information medium and special drive means influencing the reading speed were to be provided, then the power supply of said means could be correspondingly interrupted or reduced. Moreover, in contrast with the fundamental reading at twice the speed, the information medium is read at an increased speed only for the purpose of filling the buffer, and the known vibration resistance is, nevertheless, reliably achieved. Since filling of the buffer is necessary only after a restart or only after a vibration-induced interruption, the information medium can be read or driven predominantly at the normal reading speed, which corresponds to the normal speed. The operation at normal speed already results in a considerably reduced power consumption, since, on the one hand, the rotational speed of the motor is correspondingly lower and, in addition, control operations and movements of the scanning system for the purpose of finding the scanning location after the interruption due to the risk of the buffer overflowing as a result of writing at twice the speed and reading at normal speed are dispensed with. In order to reduce the rotational speed, not only is the reference frequency or the desired rotational speed value in the known CLV control loop reduced, which would still likewise require a high power consumption owing to a so-called hard rotational speed changeover, but rather it is provided to interrupt the power supply to the drive motor or at least significantly reduce it. The means provided for this purpose is preferably an electronic switch provided in the power supply line to the drive motor.

By means of the reference signal source, which can be varied in a predetermined range, for controlling the rotational speed of the drive motor, the scanning speed is set as a function of the occupancy of the buffer in such a way that writing or reading-in of data to the buffer is provided at an increased speed compared to the reading-out speed from the buffer only when the occupancy of the buffer falls below a predetermined value at the starting instant of the playback operation or on account of the track being lost. During the periods in which no track is lost and the buffer has a predetermined occupancy, the information medium is driven only at normal speed. As a result of this type of rotational speed control, scanned data are no longer read into the buffer at a constant speed or at a constant frequency. Nevertheless, the reproduction of information is not disturbed if a phase-locked loop or a so-called PLL having a large capture range is provided. Varying the reading speed without any loss in the bit timing required for the processing of the information from the information medium is made possible by means of a bit timing PLL which has a relatively large capture range. This capture range should preferably be more than ±60%. Therefore, the reproduction signal or the reproduction of information is not influenced by fluctuations in the reading speed or in the rotational speed of the drive motor of the information medium given a correspondingly large capture range in the range, for example, of from 80% to 180% of the normal value. This large capture range, which, inter alia, can also be attributed to the eight to fourteen modulation used for the data storage or data recovery, permits data to be read into the buffer at varying speeds, with the result that the rotational speed of the drive motor of the information medium can be varied within the capture range of the PLL in order to reduce the power consumption. Since the rotational speed of the drive motor can be returned to normal speed after a predetermined occupancy of the buffer has been reached, it is preferably provided, for the purpose of reducing power consumption, to disconnect the drive motor completely from the power supply during the period until the normal speed or a predetermined speed value, which may also be less than the normal speed, is reached. This disconnection is achieved by causing the connection to have a high resistance. The resulting so-called soft changeover of the rotational speed of the drive motor leads, in conjunction with the reduction in the doubled speed to the normal speed, to a considerably reduced power consumption, which permits considerably longer operation of the playback device with a set of batteries.

Although the above explanations were essentially referring to a CD as the information medium, the field of application is not restricted thereby, since in principle all digital latches and information media, including, for example, the digital videodisk or digital tapes, have a comparatively similar data structure, which enables the principle upon which the invention is based to be applied.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with reference to drawings, in which:

FIG. 1 shows a block diagram of the vibration-resistant playback device with improved control,

FIG. 2 shows a flow diagram for controlling the vibration-resistant playback device,

FIG. 3 shows a block diagram of a known vibration-resistant playback device,

FIG. 4 shows a flow diagram for controlling the improved vibration-resistant playback device as a function of two occupancy values,

FIG. 5 shows a block diagram of the vibration-resistant playback device having a reduced power consumption,

FIG. 6 shows a block diagram for the control of the vibration-resistant playback device in accordance with FIG. 5,

FIG. 7 shows a block diagram for the control of the known vibration-resistant playback device in accordance with FIG. 3, and

FIG. 8 shows a flow diagram for controlling the improved vibration-resistant playback device having a reduced power consumption.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Corresponding reference symbols are used consistently in the drawings.

In order to bridge interruptions of the read operation from the information medium 1, the known vibration-resistant playback device in accordance with FIG. 3 has a buffer 16, which is connected to a decoder 15 containing an error correction and de-interleaving unit 10. The buffer 16 is arranged directly upstream of the digital/analog converter 12, which is connected to a reproduction device 14, and is connected to a control unit 17 which is connected to the microprocessor 13 of the vibration-resistant playback device. In order to ensure disturbance-free and uninterrupted reproduction of information even during an interruption of the read operation from the information medium 1 due to vibrations, data read from the information medium 1 are written at twice the speed to the buffer 16 and are read out at normal speed. The result of this is that there is always an adequate volume of data in the buffer 16 in order briefly to bridge interruptions of the read operation from the information medium 1, and the buffer 16 is filled with data once more, following an interruption of the read operation which empties the buffer 16, in order to be prepared for another interruption. The information medium 1 is driven, for the purpose of reading at twice the speed, by a motor 3 which is operated at twice the rotational speed and is connected to a CLV servo 6. The CLV servo 6 is used to vary the rotational speed of the motor 3, which is in principle doubled in the case of the known playback device, as a function of the scanning radius in order to achieve an approximately constant reading speed. This varying of the rotational speed takes place in the scope which is conventional for the constant reading speed, and not as a function of the occupancy of the buffer 16.

The information stored on the information medium 1 is detected by a pick-up forming the scanning device 2 and is fed to a pulse-shaping and EFM demodulator unit 4. Using the pulse-shaping and EFM demodulator unit 4, in particular the digital signal which arrives from the information medium 1 and is still rounded is converted into a fairly digital signal and the timing required for the further processing of the information is generated. In this case, the EFM (eight to fourteen modulation) is provided, in particular, to permit reliable timing recovery even in the case of soft passages or pauses, in which the individual bits do not toggle between their possible states. A so-called bit timing PLL 5 is used, in particular, for this purpose. Furthermore, there are provided in the decoder 15 a subcode decoder 7, which decrypts the supplementary information contained in the subcode, and also an error correction and de-interleaving unit 10, by means of which the digital audio signal is provided in the case of a CD player. In the case of the known vibration-resistant playback device in accordance with FIG. 3, a buffer 16 designed as a DRAM is connected downstream of this error correction and de-interleaving unit 10. The audio data stored in the buffer 16 for bridging an interruption of the reading of information from the information medium 1 are then fed via a digital/analog converter 12 to the reproduction device 14. A control unit 17, which is also referred to as a shock-proof memory controller and is connected to a microprocessor 13 which organizes the control and data evaluation of the playback device, is provided for the organization of the buffer 16 or for writing data to and reading data from the buffer 16. With the known method, audio data are written to the buffer 16 until there is an interruption of the reading of information from the information medium 1 owing to a vibration or when the maximum occupancy of the buffer 16 has been reached. After an interruption, the scanning device 2 is then reset to a scanning location corresponding to the last valid subcode address, and the reading of the information medium 1 is resumed. However, since the scanned values are not present with any accuracy in the buffer 16 after the error correction and the de-interleaving and since there is no information which identifies the address of the interruption, a comparison must be carried out, until correspondence, between audio data read anew and audio data present in the buffer 16. When correspondence is established, the writing of read data to the buffer 16 is then resumed. However, in the case of very soft information sections, muting on account of a very high error rate, or in the case of repetitions having the same information content, such a comparison results in correspondence at different locations, which correspondence does not correspond to the sequence of information stored on the information medium 1.

Both the method and the arrangement of FIG. 1 and FIG. 2 have been correspondingly altered in comparison with the known vibration-resistant playback device. An essential aspect of the vibration-resistant playback device with improved control is that the reading speed from the information medium 1 is controlled by a control unit 9 as a function of a predetermined occupancy of the buffer, which is preferably arranged, in accordance with FIG. 1, as a buffer 8 upstream of the error correction and de-interleaving unit 10. Consequently, the vibration-resistant playback device in accordance with FIG. 1 does not operate at a constant doubled reading speed. In accordance with FIG. 2, use is predominantly made of a first reading speed V1, which corresponds to the conventional normal speed in playback devices without special vibration protection and hence also to the speed at which data are read from a buffer 8 or 16 for the purpose of reproducing information. This first reading speed V1 is increased to a second reading speed V2 only during the filling of the buffer 8 or 16 up to a predetermined occupancy value N %, which is less than the maximum storage capacity of the buffer 8 or 16. The occupancy value N is selected in such a way that the buffer 8 is filled only up to its maximum storage capacity, and does not overflow, during the transition from the increased second reading speed V2 to the first reading speed V1. Since only the reading speed V1 corresponds to the speed at which the buffer 8 is read out, the volume of stored data also additionally rises during the transition to the normal speed. The difference between the predetermined occupancy value N % and the maximum storage capacity is provided for this rise in occupancy. A second reading speed V2 which lies within the capture range of the bit timing PLL 5 is preferably selected to be the maximum second reading speed V2. This capture range should be more than ±60%, even though a known SONY decoder CXD2500 only has a capture range of ±4%, with the result that the second reading speed V2 can be selected as 180% of the first reading speed V1 in order to ensure rapid filling of the buffer 8 or 16. The second reading speed V2 is preferably selected to be within the capture range of the bit timing PLL 5 in order to permit, despite the change in the reading speed V1, bit timing recovery, which is necessary for the signal processing, and writing to the buffer 8 or 16 without interruption. The occupancy value N % of the buffer 8 or 16 at which the changeover between the reading speeds V1, V2 is to be performed in order to prevent an overflow of the buffer 8 or 16 is determined conclusively by the transient response of the playback device between the speeds V1 and V2 and may be, for example, 80% of the maximum storage capacity of the buffer 8 or 16. In this case, the maximum storage capacity of the buffer 8 or 16 determines the time which can be bridged without any disturbances during the occurrence of vibrations. A flow diagram corresponding to this method is illustrated in FIG. 2. In accordance with this flow diagram, the occupancy of the buffer 8 or 16 is checked during the reading of the information medium 1 at the first reading speed V1. For this purpose, the current occupancy, referred to as the RAM level, of the buffer 8 or 16 is compared with a predetermined occupancy N, which is a percentage value N % of the maximum storage capacity of the buffer 8. If the current occupancy, referred to as the RAM level, of the buffer 8 is less than the predetermined occupancy value N %, the read operation is accelerated to the second reading speed V2. The second reading speed V2 is then maintained until the current occupancy, referred to as the RAM level, of the buffer 8 is greater than the predetermined occupancy value N %. If the current occupancy, referred to as the RAM level, of the buffer 8 exceeds the predetermined occupancy value N %, the reading speed V2 is preferably reduced to the first reading speed V1. It is thus achieved that the current occupancy RAM level increases only as the speed decreases and does not rise any further when the first reading speed V1 is reached, since the writing and reading-out speeds correspond at this speed. The occupancy value N % is selected in such a way that the maximum storage capacity of the buffer 8 is not exceeded, taking account of this transient response. The fixed occupancy value N % is dependent both on the magnitude of the second reading speed V2 and on the speed at which a changeover is made between the speeds, which is influenced by the inertia of the system, and may be, for example, 80% of the maximum storage capacity of the buffer 8 or 16.

The first reading speed V1 is preferably equal to the speed used for the reproduction of information, and the second reading speed V2 is preferably increased by 80% relative to the first reading speed.

If the current occupancy RAM level is not less than the predetermined occupancy value N %, a signal is evaluated which is in principle provided by the microprocessor 13 and represents an item of information regarding whether, for example, a vibration or a so-called shock has occurred and the writing to the buffer 8 or 16 must be stopped or whether a jump is to be made to another memory location on the information medium 1 on account of an operator instruction. After shock recovery or resetting of the scanning device 2 and a successful jump, the writing to the buffer 8 is then resumed after data synchronization has been carried out. The shock can also be detected and processed or corrected if the occupancy=N % has not yet been reached. The time available for correction depends on the current occupancy.

In accordance with a second design illustrated in FIG. 4, a first occupancy value N1 and a second occupancy value N2 are used as the predetermined occupancy value N %, the second occupancy value N2 being greater than the first occupancy value N1. FIG. 4 and FIG. 2 are identical in respect of all the other parts and of the fundamental sequence, so that it is possible to limit the explanations to the difference between them. The use of a first and a second predetermined occupancy value N1, N2 for controlling the reading speed in vibration-resistant playback devices is particularly advantageous with regard to a lower number of changeovers between the reading speeds V1, V2. With a first and a second predetermined occupancy value N1, N2 for controlling the reading speed, a hysteresis corresponding to the difference between the occupancy values N1, N2 is formed, which has the result that an acceleration is made from the first reading speed V1 to the second reading speed V2 only in the event of a lower occupancy value N1, and the reading speed V2 is reduced to the first reading speed V1 only when a predetermined upper occupancy value N2 is reached or exceeded. Under comparable conditions, the number of changeovers decreases as a result, a greater running smoothness is achieved and, at the same time, the power consumption is reduced further.

In addition to reducing the number of returns and decreasing the power consumption, a further aspect is the synchronization or the seamless writing of data to the buffer 8, in accordance with the information stored on the information medium 1, following an interruption.

Although the abovementioned exemplary embodiments can be combined, as regards the synchronization, with the known synchronization method based on the comparison of audio or reproduction information data, a further design is specified, which can be used to increase the synchronization reliability further. It should be mentioned that the number of necessary synchronization operations have already been reduced by a smaller number of resets of the scanning device 2, which is achieved by preventing the buffer 8 or 16 from overflowing. Since the writing to the buffer 8 or 16 is interrupted only in the event of a shock- or vibration-induced interruption of the reading from the information medium 1, a higher reliability of the known synchronization has already been achieved, but it can be increased further by another type of synchronization. The control unit 9, which has already been mentioned in the above explanations, for controlling the reading speed V1, V2 of the information medium 1 as a function of the predetermined occupancy of the buffer 8 or 16 is preferably designed as part of the decoder 11 of the playback device, as a result of which subcode information detected from the information medium 1 can advantageously be used for the signal processing and control of the vibration-resistant playback device. A first contribution is made by the use of reading speeds V1, V2 within the capture range of the bit timing PLL 5, enabling uninterrupted writing of data to the buffer 8 or 16 despite a change in the reading speed.

Furthermore, the buffer 8 is arranged, in accordance with the design illustrated in FIG. 1, between a pulse-shaping and EFM demodulator unit 4 and the error correction and de-interleaving unit 10. This arrangement of the buffer 8 advantageously permits the use of address information for the purpose of synchronization. Although the address information contained in subcode information occurs only with large spacings and the reading speed is temporarily changed, said address information can be used on account of the time base compensation function based on the buffer 8. The starting point of this synchronization is formed by a valid subcode, the address information of which can be used as a reference both for the location of the interruption on the information medium 1 and for the last valid data in the buffer 8 and the writing to the buffer 8. Whenever a valid subcode occurs, that is to say whenever the CIRC check has not signalled an error, the microprocessor 13 evaluating the subcode passes the information that the last subcode was valid to the control unit 9. The CIRC check is an error correction code developed by Sony, CIRC representing the abbreviation of Cross Interleave Reed Solomon Code. The first address of the subcode, that is to say the address of the synchronization bytes S0, S1, is always stored in the control unit 9. In this way, a location of the data read from the information medium 1 is localized. After the control unit 9 has received the information regarding the presence of a valid subcode, the address is preferably stored in a register of the control unit. This stored value then forms the reference when a vibration occurs. When a vibration or a so-called shock occurs, the last valid address in the control unit 9 is thereby stored. Consequently, there are items of information regarding the point on the information medium at which an interruption took place and regarding the address at which writing to the buffer 8 took place and which was still valid. After the interruption due to a shock, the scanning or reading unit is returned to a location on the information medium 1 prior to the interruption. This location may be the last valid location or a location at the point a plurality of subcodes before the interruption. If the scanning device 2 is guided, for example, to a location which was five subcodes before the interruption, then it is known that the shock occurred five subcodes later, the address of which shock is known on account of the storage in the control unit 9. Starting from this address, a calculation is then made back to an address which is located further back, in this example, by five times the number of bytes between the subcodes, with the result that the location in the buffer 8 starting at which the previous buffer contents can be overwritten is localized.

On the other hand, it is possible to move to the subcode at which the shock occured, and to start with the stored address. The renewed writing always begins at a synchronization byte, even if, subsequently, other valid data should still be present. This synchronization to an absolute address ensures absolutely reliable synchronization, as a result of which a chronological offset is in principle precluded.

Using the address which identifies the location of an interruption on the information medium 1 and in the buffer 8, it is also possible for the synchronization and the writing to the buffer 8 following an interruption to be carried out even before the address of the interruption, since the spacing between the address read anew and the stored address of the interruption can be calculated. The data following the address are then overwritten, thus reducing the time to synchronization. Although the above explanations regarding the synchronization were essentially referring to an information medium 1 in the form of a CD, the field of application is not restricted thereby, since in principle all digital latches and information media, including, for example, the digital videodisk or digital tapes, have a comparatively similar data structure which enables the principle described to be applied. Consequently, the application is also possible in connection with magnetic or mechanical scanning devices and also in connection with information media in the form of tape and other two-dimensional information media. On account of the arrangement of the buffer 8 between the EFM demodulator 4 and the de-interleaving and error correction unit 10 which provides the digital audio information, use can be made of an ARAM, which is less expensive than a DRAM, as the buffer 8. The use of a ARAM or audio RAM, which may be partially defective, as the buffer 8, by which the synchronization following an interruption is also carried out, is made possible by the arrangement upstream of the error correction unit 10.

A further aspect is the rapid availability of data for reproduction after starting the playback device. If the vibration-resistant playback device presented is started, data from the information medium 1 are available in the buffer 8 or 16 for the purpose of reproduction as early as when the normal speed corresponding to the normal or first reading speed V1 is reached, and the reproduction does not have to be delayed until there has been an acceleration to the doubled reading speed of the known playback device, as a result of which, as a further advantage, a shorter access time is achieved.

FIG. 7 shows a block diagram for the control of the known vibration-resistant playback device in accordance with FIG. 3, relating in particular to the control of the rotational speed of the drive motor M. In order to read the information medium 1 at a constant reading speed, use is made of a constant reference frequency FR which is compared in a summing point + with an item of speed information SPI in order to form an error signal ES. The constant reference frequency FR corresponds, in the case of the known vibration-resistant playback device, to twice the normal reading speed or twice the speed at which the buffer 16 is read out for reproducing information, so that the buffer 16 is refilled as quickly as possible following an interruption of the writing to said buffer. The current speed information SPI of the drive motor M of the information medium 1 is derived from the bit timing frequency of the data stream read from the information medium 1, with the result that the rotational speed DSPO of the drive motor M is controlled in accordance with a constant, doubled reading speed. For this purpose, a controller CLV Servo Controller is provided, and is connected to the microprocessor MPU or 13 and a driver D which controls the drive motor M. The rotational speed DSPO of the drive motor M in this case corresponds to twice the rotational speed which would be necessary to read at normal speed.

Both the method and the arrangement of FIG. 5, FIG. 6 and FIG. 8 have been correspondingly altered in comparison with the known vibration-resistant playback device. One aspect of the vibration-resistant playback device having a reduced power consumption is that the reading speed from the information medium 1 is controlled by a control arrangement 9 as a function of a predetermined occupancy of the buffer, which is preferably arranged, in accordance with FIG. 5, as a buffer 8 upstream of the error correction and de-interleaving unit 10. Consequently, the vibration-resistant playback device in accordance with FIG. 5 does not operate at a constant doubled reading speed. In accordance with FIG. 6 and FIG. 8, use is predominantly made of a first reading speed SSPO, which corresponds to the conventional normal speed in playback devices without special vibration protection and hence also to the speed at which data are read from a buffer 8 or 16 for the purpose of reproducing information. This first reading speed SSPO is increased to a second reading speed VSPO only during the filling of the buffer 8 or 16 up to a predetermined occupancy value N %, which is preferably less than the maximum storage capacity of the buffer 8 or 16. The occupancy value N is selected in such a way that the buffer 8 is filled only up to its maximum storage capacity, and does not overflow, during the transition from the increased second reading speed VSPO to the first reading speed SSPO. Since only the first reading speed SSPO corresponds to the speed at which the buffer 8 is read out, the volume of stored data also additionally rises during the transition to the normal speed. The difference between the predetermined occupancy value N% and the maximum storage capacity is provided for this rise in occupancy. A second reading speed VSPO which lies within the capture range of the bit timing PLL 5 is preferably selected to be the maximum second reading speed VSPO. This capture range should be more than ±60%, even though a known SONY decoder CXD2500 only has a capture range of ±4%, with the result that the second reading speed VSPO can be selected as 180% of the first reading speed SSPO in order to ensure rapid filling of the buffer 8 or 16. The second reading speed VSPO is preferably selected to be within the capture range of the bit timing PLL 5 in order to permit, despite the change in the reading speed SSPO, bit timing recovery, which is necessary for the signal processing, and writing to the buffer 8 or 16 without interruption. The occupancy value N % of the buffer 8 or 16 at which the changeover between the reading speeds SSPO, VSPO is to be performed in order to prevent an overflow of the buffer 8 or 16 is determined conclusively by the transient response of the playback device between the speeds SSPO and VSPO and may be, for example, 80% of the maximum storage capacity of the buffer 8 or 16. In this case, the maximum storage capacity of the buffer 8 or 16 determines the time which can be bridged without any disturbances during the occurrence of vibrations. A flow diagram corresponding to this method is illustrated in FIG. 5. In accordance with this flow diagram, the occupancy of the buffer 8 or 16 is checked during the reading of the information medium 1 at the first reading speed SSPO. For this purpose, the current occupancy, referred to as the RAM level, of the buffer 8 or 16 is compared with a predetermined occupancy N, which is a percentage value N % of the maximum storage capacity of the buffer 8. If the current occupancy, referred to as the RAM level, of the buffer 8 is less than the predetermined occupancy value N %, the read operation is accelerated to the second reading speed VSPO. The second reading speed VSPO is then maintained until the current occupancy, referred to as the RAM level, of the buffer 8 is greater than the predetermined occupancy value N %. If the current occupancy, referred to as the RAM level, of the buffer 8 exceeds the predetermined occupancy value N %, the reading speed VSPO is preferably reduced to the first reading speed SSPO. It is thus achieved that the current occupancy RAM level increases only as the speed decreases and does not rise any further when the first reading speed SSPO is reached, since the writing and reading-out speeds correspond at this speed. The occupancy value N % is selected in such a way that the maximum storage capacity of the buffer 8 is not exceeded, taking account of this transient response. The fixed occupancy value N % is dependent both on the magnitude of the second reading speed VSPO and on the speed at which a changeover is made between the speeds, which is influenced by the inertia of the system, and may be, for example, 80% of the maximum storage capacity of the buffer 8 or 16.

The first reading speed SSPO is preferably equal to the speed used for the reproduction of information, and the second reading speed VSPO is preferably increased by 80% relative to the first reading speed.

If the current occupancy RAM level is not less than the predetermined occupancy value N %, a signal is evaluated which is in principle provided by the microprocessor 13 and represents an item of information regarding whether, for example, a vibration or a so-called shock has occurred and the writing to the buffer 8 or 16 must be stopped or whether a jump is to be made to another memory location on the information medium 1 on account of an operator instruction. After shock recovery or resetting of the scanning device 2 and a successful jump, the writing to the buffer 8 is then resumed after data synchronization has been carried out. The shock can also be detected and processed or corrected if the occupancy=N % has not yet been reached. The time available for correction depends on the current occupancy.

In accordance with a second design, not illustrated, a first occupancy value N1 and a second occupancy value N2 are used as the predetermined occupancy value N %, the second occupancy value N2 being greater than the first occupancy value N1. The designs are identical in respect of all the other parts, so that it is possible to limit the explanations to the difference between them. The use of a first and a second predetermined occupancy value N1, N2 for controlling the reading speed in vibration-resistant playback devices is particularly advantageous with regard to a lower number of changeovers between the reading speeds SSPO, VSPO. With a first and a second predetermined occupancy value N1, N2 for controlling the reading speed, a hysteresis corresponding to the difference between the occupancy values N1, N2 is formed, which has the result that an acceleration is made from the first reading speed SSPO to the second reading speed VSPO only in the event of a lower occupancy value N1, and the reading speed VSPO is reduced to the first reading speed SSPO only when a predetermined upper occupancy value N2 is reached or exceeded. Under comparable conditions, the number of changeovers decreases as a result, a greater running smoothness is achieved and, at the same time, the power consumption is reduced further.

The changeover from a first reading speed SSPO to a second reading speed VSPO can be performed, in accordance with FIG. 6, at a variable reference frequency VR, which is set by the microprocessor MPU or 13. This is a first difference from the block diagram, indicated in FIG. 7, for the control of the drive motor M of the known vibration-resistant playback device in accordance with FIG. 3. Despite the variable reference frequency VR, a controller CLV Servo Controller is provided, by means of which the rotational speed of the drive motor M is set for a constant reading speed irrespective of the scanning radius. This is necessary because the rotational speed of the drive motor M must be set differently as a function of the scanning radius for a constant reading speed. The control of the rotational speed of the drive motor M, which is based on a comparison of the current speed information SPI with a reference, is coordinated by an actuating device which is formed by the microprocessor MPU,13 connected to the controller CLV Servo Controller and the reference frequency VR which can be set variably by the said microprocessor. In principle, this would permit a changeover between different reading speeds SSPO and VSPO. However, in order additionally to decrease the power consumption and the outlay, there is provided in the connection to the drive motor M in accordance with FIG. 6 a switch SW, which is also illustrated in FIG. 5. This switch SW enables the power supply to be interrupted, or at least greatly reduced, particularly during the reduction of the rotational speed of the drive motor M, if an electronic switch SW in the form of a semiconductor which can be controlled in respect of its conductivity is used as the switch SW. As a result, no power is required for the drive motor M during the reduction of the rotational speed, and the power consumption is reduced. This switch SW may appear to represent an increase in the outlay in comparison with the known solution, but in fact it contributes to reducing the outlay. This is a result of the fact that the control of the rotational speed, in particular the controller CLV Servo Controller, would otherwise have to be provided with different time constants. Specifically, on the one hand deviations from a predetermined reading speed must be corrected as quickly as possible by the controller CLV Servo Controller and, on the other hand, the reversal between the reading speeds SSPO and VSPO should take place as slowly as possible in order to keep the power consumption and the requirements on the PLL low. A hard changeover would lead to an increased power consumption. Therefore, the switch SW is advantageous not only from the point of view of a lower power consumption. It has a double function and is preferably controlled by the controller CLV Servo Controller or the microprocessor MPU, 13. In accordance with FIG. 6, the switch SW can also be designed, by combination with the driver D, as a unified assembly D+SW.

The method underlying the improved vibration-resistant playback device having a reduced power consumption is summarized once more using the flow diagram illustrated in FIG. 8.

In accordance with the illustration, the starting point is a normal speed SSPO which corresponds to the normal reading speed SSPO of the information medium and hence essentially accords with the speed at which the buffer is also read out for reproducing information. If the occupancy RAM level of the buffer were to fall below a predetermined occupancy N %, the reading speed SSPO is accelerated until a maximum reading speed VSPO determined by the capture range of the PLL is reached, or until a predetermined occupancy M % of the buffer is exceeded. The occupancy M % preferably does not correspond to the maximum storage capacity of the buffer, it can be identical to the predetermined occupancy N % or correspond to an occupancy N2. After the occupancy M % is exceeded, the drive motor M with the motor OFF is disconnected from the power supply, with the result that there is no more consumption. For this purpose, the switch SW is opened. There is then monitoring to see if the speed falls below a speed Q which preferably corresponds to the normal reading speed SSPO but may also be selected to be less than the normal speed SSPO within the capture range of the PLL. At the same time, the occupancy RAM level of the buffer is monitored to see whether it is still larger than a predetermined occupancy N %. During the period in which the rotational speed of the drive motor or the reading speed does not fall below a predetermined speed Q and the occupancy of the buffer also does not fall below a predetermined occupancy N %, the drive motor M can be disconnected from the power supply or from the driver D in order to reduce the power consumption. Only when one of the abovementioned parameters is undershot does the return to normal speed take place by connecting the power supply which drives the drive motor M. If a shock were to occur or if a jump to another scanning location were to be necessary, the further writing to the buffer is stopped and the reset procedure to the location of the interruption or a track jump is initiated and the writing is resumed after synchronization, the reading being carried out at normal speed SSPO provided that the occupancy of the buffer has not fallen below a predetermined occupancy N %.

When the drive motor M is disconnected, the rotational speed is reduced only gradually as a function of the inertia caused by the mass of the rotor, of the disk turntable and of the information medium, with the result that this can advantageously be used for reducing the power consumption.

In addition to reducing the number of returns and decreasing the power consumption, a further aspect is the synchronization or the seamless writing of data to the buffer 8, in accordance with the information stored on the information medium 1, following an interruption.

Although the abovementioned exemplary embodiments can be combined, as regards the synchronization, with the known synchronization method based on the comparison of audio or reproduction information data, a further design is specified, which can be used to increase the synchronization reliability further. It should be mentioned that the number of necessary synchronization operations have already been reduced by a smaller number of resets of the scanning device 2, which is achieved by preventing the buffer 8 or 16 from overflowing. Since the writing to the buffer 8 or 16 is interrupted only in the event of a shock- or vibration-induced interruption of the reading from the information medium 1, a higher reliability of the known synchronization has already been achieved, but it can be increased further by another type of synchronization. The control arrangement 9, which has already been mentioned in the above explanations, for controlling the reading speed SSPO, VSPO of the information medium 1 as a function of the predetermined occupancy of the buffer 8 or 16 is preferably designed as part of the decoder 11 of the playback device, as a result of which subcode information detected from the information medium 1 can advantageously be used for the signal processing and control of the vibration-resistant playback device. A first contribution is made by the use of reading speeds SSPO, VSPO within the capture range of the bit timing PLL 5, enabling uninterrupted writing of data to the buffer 8 or 16 despite a change in the reading speed.

Furthermore, the buffer 8 is arranged, in accordance with the design illustrated in FIG. 5, between a pulse-shaping and EFM demodulator unit 4 and the error correction and de-interleaving unit 10. This arrangement of the buffer 8 advantageously permits the use of address information for the purpose of synchronization. Although the address information contained in subcode information occurs only with large spacings and the reading speed is temporarily changed, said address information can be used on account of the time base compensation function based on the buffer 8. The starting point of this synchronization is formed by a valid subcode, the address information of which can be used as a reference both for the location of the interruption on the information medium 1 and for the last valid data in the buffer 8 and the writing to the buffer 8. Whenever a valid subcode occurs, that is to say whenever the CIRC check has not signalled an error, the microprocessor 13 evaluating the subcode passes the information that the last subcode was valid to the control arrangement 9. The CIRC check is an error correction code developed by Sony, CIRC representing the abbreviation of Cross Interleave Reed Solomon Code. The first address of the subcode, that is to say the address of the synchronization bytes S0, S1, is always stored in the control arrangement 9. In this way, a location of the data read from the information medium 1 is localized. After the control arrangement 9 has received the information regarding the presence of a valid subcode, the address of the buffer 8 is preferably stored in a register of the control unit. This stored value then forms the reference when a vibration occurs. When a vibration or a so-called shock occurs, the last valid address in the control arrangement 9 is thereby stored. Consequently, there are items of information regarding the point on the information medium at which an interruption took place and regarding the address at which writing to the buffer 8 took place and which was still valid. After the interruption due to a shock, the scanning or reading unit is returned to a location on the information medium 1 prior to the interruption. This location may be the last valid location or a location at the point a plurality of subcodes before the interruption. If the scanning device 2 is guided, for example, to a location which was five subcodes before the interruption, then it is known that the shock occurred five subcodes later, the address of which shock is known on account of the storage in the control arrangement 9. Starting from this address, a calculation is then made back to an address which is located further back, in this example, by five times the number of bytes between the subcodes, with the result that the location in the buffer 8 starting at which the previous buffer contents can be overwritten is localized.

Using the address which characterizes the location of an interruption on the information medium 1 and in the buffer 8, it is also possible for the synchronization and the writing to the buffer 8 following an interruption to be carried out even before the address of the interruption, since the spacing between the address read anew and the stored address of the interruption can be calculated. The data following the address are then overwritten, thus reducing the time to synchronization.

A further aspect is the rapid availability of data for reproduction after starting the playback device. If the vibration-resistant playback device presented is started, data from the information medium 1 are available in the buffer 8 or 16 for the purpose of reproduction as early as when the normal speed corresponding to the normal or first reading speed SSPO is reached, and the reproduction does not have to be delayed until there has been an acceleration to the doubled reading speed of the known playback device, as a result of which, as a further advantage, a shorter access time is achieved.

Although the above explanations regarding the synchronization were essentially referring to an information medium 1 in the form of a CD, the field of application is not restricted thereby, since in principle all digital latches and information media, including, for example, the digital video disk or digital tapes, have a comparatively similar data structure which enables the principle described to be applied. Consequently, the application is also possible in connection with magnetic or mechanical scanning devices and also in connection with information media in the form of tape and other two-dimensional information media. 

What is claimed is:
 1. Vibration-resistant playback device with reduced power consumption for providing information signals from an information medium during an interruption of the reading of information stored on said information medium comprising;data reading means for reading data from said information medium, driven means, responsive to a drive signal from a driving means, for driving said information medium with respect to the data reading means, buffer memory means for receiving reproduced data read from the information medium by the data reading means, the reproduced data being written into said buffer memory at a varying reading speed which is used for reading data from said information medium, and said varying reading speed varying from a reading speed which corresponds to the reading speed at which said buffer is read out, for providing information signals from the information medium to a faster reading speed until a predetermined occupancy of said buffer is reached, switching means for selectively switching off power to the driving means so that the driving means does not provide the drive signal to the driven means, and control means, in accordance with said predetermined occupancy of said buffer means, for controlling an on/off switching operation of the switching means for varying the reading speed between a reading speed which corresponds to the reading speed at which said buffer is read out for providing information signals from the information medium, and the faster reading speed.
 2. Vibration-resistant playback device according to claim 1, wherein when the predetermined occupancy of said buffer memory means, said control means control the switching operaion of the switching means such that a reading speed at which said data is written into said buffer memory corresponds to said reading speed at which said data read out from the buffer memory, wherein said control means includes a microprocessor and a reference, for setting different reading speeds in the range of said varying reading speed.
 3. Vibration-resistant playback device according to claim 2, wherein the reference comprises a reference frequency source for setting different reading speeds from the information medium by means of the microprocessor which includes a reference frequency source which can be variably set by the microprocessor.
 4. Vibration resistant playback as defined in claim 1 wherein said control means sets a first reading speed and a second reading speed of the information stored on the information medium, which are both different from zero, as a function of the predetermined occupancy of the buffer.
 5. Vibration resistant playback device as defined in claim 1, wherein the driven means comprises a spindle motor serving as a turntable for said information medium.
 6. Vibration-resistant playback device for providing information signals from an information medium during an interruption of the reading of information stored on said information medium by storing read data in a buffer memory and having reduced power consumption comprisingdata reading means for reading data from said information medium, driven means for receiving a drive signal from a driving means, for driving said information medium with respect to the data reading means, buffer memory means for receiving reproduced data read from the information medium by the data reading means the reproduced data being written into said buffer memory at a varying reading speed which is used for reading data from said information medium, and said varying reading speed varying from a reading speed which corresponds to a reading speed at which said buffer is read out for playback to a faster reading speed until a predetermined occupancy of said buffer is reached, control means, in accordance with said predetermined occupancy of said buffer means for varying the reading speed between a reading speed which corresponds to the reading speed at which said buffer is read out for playback and the faster reading speed.
 7. Vibration resistant playback device according to claim 6, wherein said control means sets a first reading speed and a second reading speed of the information stored on the information medium which are both different from zero, as a function of the predetermined occupancy of the buffer.
 8. Vibration-resistant playback device according to claim 6 wherein when said predetermined occupancy of said buffer is reached, the control means controls an on/off switch such that the drive means supplies the drive signal to the driving means for a reading speed which corresponds to the reading speed at which the buffer is read out for playback.
 9. Vibration-resistant playback device for processing information signals from an information medium during an interruption of the reading of information stored by said information medium by storing read data in a buffer memory and having reduced power consumption comprising:data reading means for reading data from said information medium, driven means, provided with a drive signal from a driving means, for driving said information medium with respect to the data reading means, buffer memory means, for receiving data read from the information medium by the data reading means, the reproduced data being written into said buffer memory at a speed varying from said information medium, said varying reading speed varying from a reading speed which corresponds to the reading speed at which said buffer is read out for playback to the faster reading speed until a predetermined occupancy of said buffer is reached, control means, in accordance with said predetermined occupancy of said buffer for varying the reading speed between a reading speed which corresponds to a reading speed at which said buffer is read out for playback and a faster reading speed, wherein said control means controls said data reading means on and said driven means off during reducing said faster reading speed to a reading speed, which corresponds to a reading speed at which said buffer reads out for playback.
 10. Vibration-resistant playback device according to claim 9 comprising:switching means for selectively switching off power to the driving means so that the driving means does not provide the drive signal to the driven means, and said data reading means reads data from said information medium during an off state of said switching means. 